Assionobs



E. C. BALLMAN ET AL PROJECTING APPARATUS July-.17, 192s. Re. 17,037

Original Filed Aug. 6, 1914 2 W mtm'essi' a;

Reissued July 17, 1928.

UNITED STATES PATENT orrics.

- EDWIN C. BALLHAH, OF ST. LOUIS, AND EDWARD I. EVEBS, OI OVERLAND, IIISSOURI,

ASSIGNOBS. BY HESNE ASSIGNMENTS, TO ACME MOTION PICTURE PROJECTOR (X)!- PANI, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

rnoiac'rme uruwrus.

Original'lo. 1,275,120, dated August a, ma, Scrlalllo. $55,426, men August a, memllaflu mrelsne fled July 16,1927.

This invention relates to projecting apparatus.

The ordinary optical lantern, used 1n 'stereopticon or moving. picture machines comprises a source of light, a condenser adapted to concentrate the light on the slide or film,'and a projectin lens adapted to procollected and projected on the screen. I'n

ject an image of the ject on theslide or film on ;a screen, The source of light is necessarily positioned some distance from the condenser, and the condenser, therefore, receives only the light represented by the 'solid angle having the source of light as the apex, and as a result, therefore, in the ordinary projecting apparatus only about 3 per cent of the total light. of the source view of the fact that only a small percentage of-the-total light can be utilized, the intensity of this source must be very great, and it is, therefore, necessary to utilize a high candle power source, suchas an arc. The are must, however, be placed a considerable distance from the condenser to'avoid breakage, thereby causing the solid angle 'to be small; in addition, "the high temperaflammable film is used. Apart from the low effective efficiency of this apparatus and the danger involved in its operation, the arc is necessarily an unsteady source of light, which requires constant regulation, which regulation can only'be accomplished by hand and, therefore, requires for its operation, exceptionally skilled operators; and even then the image will be unsteady.

Some of the objects of this invention therefore are, to rovide. a projecting apparatus which wil obviate the disadvantages of the present construction, which is characterized by high efficiency, constancy of operation, which requires practically no attention, and in which the danger from fire is entirely eliminated. More specifically stated, the objects of this invention are, to provide a projecting apparatus, in which the source of light is an electric light bulb having a portion thereof formed with an ellipsodialreflector,which is constructed and arranged with respect to Serial 1o. scam. the source of light and the object to be projected to concentrate the major part of the ight from said source on the object in such a manner that the object will be illuminated uniformly.

Further objects willappear from the detail description taken in connection with the accompanyin drawing.

The figure 1s a diagram of a projecting apparatus constructed 1n accordance with this invention.

Referring now, to the figure, B--C repreof light, 16 the object (slide or film),-and 17 the projefit-ing lens. A reflector 45 comprising an e ipsoid formed by revolvmg' ellipse about B-G i1s the axis of revoluti'on, is so arranged that one of its foci F is positioned at the source of light 15, while its ject 16. Now, in an ellipsoid, a ray originatin at one focus and incident on the ellipsoidal surface will be reflected back to the other focus. It, therefore, follows that, when a source of light is positioned at one focus of an elli soidal reflector, the total light will be re ected back and come to a focus at theother focus; .If, therefore we utilize an ellipsoidal reflector, pla as shown in the figure and withthe' reflecting surface extending behind said source and also beyond the source, the major part of the light from said source will be concentrated at the other focus.- The proportion of the total light emitted, concentrated at' the other focus, increases as the reflecting surface is some the axis of the apparatus, 15 the source extended beyond or in front of the source of light, but it will be noted that the major part of the emitted light is thus concentrated when one-half or evenfone fourth of a complete eclipse is used.

If the object 16 is placed in the concentrated beam of light,'either to the left or to the right of the focus F, this object will receive the major part of the li ht emitted by the source. As amatter of act, taking both the reflected and the direct illumination, the object will receive practically all of the light from the source. The image the object so illuminated is projected-by the projecting lens 17 on the screen.

to. other focus F is positioned adjacent the ob- With this construction, therefore, practically all of the light emitted from the source will be concentrated ;on the object so that there is'no loss, and the efficiency will, therefore, be exceedingly high. It will, therefore,'be obvious that, with this construction, the intensity of the source can be very much less than the intensity with the prior con-- struction, which utilized only a small proportion of the light emitted. With this construction, therefore, a source of light having a'candle power of 100 will result in an image havin the same brightness as the image produce by the prior construction, when a source, such as an arc, having a candle ower of 2000 is used.

The gure shows a construction in which the elliptical reflector 45 forms the bulb for the source of light. In this construction the foci are shown at F, F, the source of light (filament) being positioned atone focus F, and the li ht from this source coming to a focus at 'and being concentrated on the object, 16. The bulb, with the exception of the surface boundedby the line 46 representing the issuance of the conical beam of light concentrated on the object, is silvered to form a reflecting surface, but is left 'unsilvered where the conical beam of light i..'sues. This construction is of. advantage in small units, since the bulb there performs the double function of a bulb and a concentrator.

In the construction shown in the drawin the reflector 45 is a simple ellipsoid. This bulb may, however, be a compound ellipsoid of the form shown and described in Figures ftion accomplishes its object. 1 An apparatus -5 to 12 inclusive of our companion reicsue application, S. N. 401,276, filed August 4, 1920. In the first cases,- the filament will be closely coiled, while in the latter cases this filament will be a fin It will, therefore, eseen that the invenis produced in which the major part and substantially all of the light emitted by the source is concentrated on the object whose image is to be projected on the screen. The efiiciency of the apparatus will, therefore,

j be very high, permitting the use of a low candle power source of light.

Such a low candle: power source not only lessens the danger from fire, but also protects the apparatus. Since this construction permits the use of an incandescent filament adapted to operate from'a constant voltage system,

the-intensity of illumination may be kept and it is, therefore, to be understood that this invention is not' to be limited to the specific constructionshown and described.

Having thus described the invention,

what is claimed is:

1. A projecting apparatus comprising an electric light bulb having a portion thereof formed as an ellipsoid reflector with the filament at one focus.

2. A projecting apparatus comprising an electric light bulb having a portion thereof formed as areflect'or comprising a surface of revolution conztructed and arrangedto concentrate light from the filament on an I object.

3. A projecting apparatus comprising an electric light bulb, ellipsoidal in shape, with the filament atone focus the bulb being constructed and arranged to concentrate upon an object adjacent the other focus, substantially all of the rays from the filament except such as impinge upon the object directly from the filament.

4. A projecting apparatus comprising an electric light bulb having a portion thereof formed as an ellipsoid reflector with the filament at one focus, said reflector being constructed and arranged to concentrate the light uniformly on an object atthe other focus. 5. A projecting apparatus comprising an electric light bulb having a portion thereof formed as a reflector comprising a surface of revolution constructed and arranged to conccntratelight from the filament uniformly on an object.

6. A projecting apparatus comprising an electric light bulb ellipsoidal in shape with the filament at one focus, the bulb being constructed and arranged to concentrate uniformly upon an object adjacent the other focus substantially all of the rays from the filament except such as impinge upon the object directly from the filament.

In testimony whereof we affix our signatures.

EDWIN C. BALLMAN. ,EDWARD P. EVERS. 

